Steps to reproduce:
Run a test instance and modify Description field of a step. Add a screenshot to the Actual result of a step.
Save the run. You get a pop-up asking "Would you like to save the changes into test planning?". Select Yes.
Then go to see the test case in test plan side. The screenshot that you attached to the Actual result of a run step is in the test case design step.
This behavior is not correct. The attachment should not exist in the test case design step, only in the run step.